It's not just the oil weight. It's the pistons and how many holes they have in them, how big the holes are, the spring rate, the pre-load, etc that affects that stuff.
You want it setup to keep your chassis from slapping the ground, based on the terrain you're driving in, and any jumping you...
Looks like a whole lotta fun! But I think that is more of a rock racer type vehicle? The truck the OP is playing with here is a Redcat if I remember correctly, but not sure what you'd call it now. Maybe in between a bouncer or a racer I guess. Here's a pic from his other thread.
A rock bouncer needs quick movement to get the tires planted when flying over bumps and obstacles. So a thin shock fluid that allows the springs to rebound the shocks quickly would be what I went after. I would maybe start with 30w shock oil and I would want springs just firm enough to get about...